Lithium and Nickel Contamination in Plants and the Environment

The following sections are included:

• Preface
• About the Editors
• Abbreviations
• Contents

The chapter deals with some important aspects of the relationship of lithium and nickel with the ecosystem, which consists mainly of soil, water, plants and air. Some aspects of lithium and nickel use in the energy industry are also mentioned. We begin by considering the fact that the metallic elements lithium and nickel, either alone or in the form of their chemical compounds, are currently considered potential energy materials whose applicability is increasing with the transition to the mass use of electricity and batteries for powering motor vehicles. Both lithium and nickel are commonly found in nature. Even in relatively low concentrations, their presence is very dangerous or even toxic to some animals and biological organisms. On the other hand, certain plants and animals are a natural part of ecosystems and are unable to survive with-out their presence because they are vital to them. This contradiction and its implications form the main content of this chapter. The most significant effects of lithium and nickel in the environment, particularly in soil, water and plant systems, are presented. The interconnectedness between soil, water and plants is shown in relation to each other. Some of the analytical methods used for the detection of lithium and nickel are also given. In addition, some specific results are presented, which are not intended to specify particular locations in the field, but rather to highlight the ability of researchers to monitor the presence of lithium and nickel in the environment and to create conditions for their removal and possible reuse.

Lithium (Li) is taking frontline in electronic items and vehicles world-wide. Great uses of Li draw attention and are in demand everywhere, hence production also increases daily. The major problem with Li is its toxicity, which eventually enters human and animal life via the food chain. It is non-degradable and has a long shelf-life — it can sustain anywhere for a more extended period but causes much toxicity to the host. Removal of Li is a big challenge, and expensive methods need to be employed. Thus, environmentalists came up with a sustainable approach called phytoremediation — the use of plants to clean up hazardous contaminants. In this method, the plant, or hyperaccumulator, grows on Li-contaminated soils and absorbs a higher concentration of Li without compromising its own immunity. In this chapter, we reviewed the source, pathway of contamination and remediation of Li using plant species.

Lithium (Li) is considered an emerging metal contaminant in the environment. To better prepare for the challenges to crop productivity from Li pollution, it is necessary to have a better understanding of the physiological basis/mechanisms of the responses of plants to Li stress. The overview presented here of the toxic effects of Li shows that different plants may exhibit variations in the relationship between Li bioaccumulation and the severity of growth inhibition and reduction in the contents of the different photosynthetic pigments. To deepen our understanding of how different plants respond to Li exposure, many studies have focussed on the increase in oxidative stress, which could cause damage to biomolecules, such as membrane lipids and proteins. These damages could be translated into growth inhibition effects and the loss of photosynthetic pigments. In addition, since various mineral nutrients, such as K, Ca and Mg, play vital roles in various metabolic reactions and pathways, alterations in mineral contents in plants exposed to Li could result in metabolic reprogramming leading to growth alterations. It is proposed here that gene expression changes, particularly those involved in plant hormone metabolism and transport as well as autophagy, could also underlie the physiological responses of plants to Li stress.

Nickel (Ni) is an essential, naturally occurring micronutrient required for various metabolic processes in plants, such as ureolysis, hydrogen metabolism, methane biogenesis and acetogenesis, since it is an important component of the enzymes glyoxalases, ureases, superoxide dismutases, hydrogenases, etc. Ni constitutes the active site of two metalloenzymes, i.e., urease and hydrogenase, in plants, which are involved in nitrogen (N) metabolism. Urease is responsible for the breakdown of urea into ammonia and carbon dioxide, while hydrogenase catalyses the oxidation of molecular hydrogen and recovers the energy for the reduction of enzymes. Elevated levels of Ni (≥20 mg kg⁻¹) in the soil pose a significant threat to the agricultural productivity of crop plants world-wide owing to their extreme toxicity. Consequently, Ni has now been ranked 57th in priority hazardous substances by the American Agency for Toxic Substances and Disease Registry (ATSDR, 2022). The common symptoms of Ni toxicity in plants include reduced germination, declined shoot and root growth, membrane damage, reduced nutrient absorption and abnormal flower shape. All these toxic effects result in reduced photosynthesis and respiration rates, loss of key osmolytes, etc., which cause oxidative stress and ultimately reduce the yield of crops. In addition, excess Ni has a negative impact on legume–rhizobia symbiosis by affecting nodulation potential and N₂-fixation processes, as well as decreasing ureides biosynthesis. However, significant variations in terms of Ni metal-induced sensitivities among various crop plants have been observed at various levels. Therefore, this chapter reviews the updated information regarding Ni stress-induced physiological, biochemical and molecular responses in crop plants, especially legumes.

Lithium (Li) and nickel (Ni) are two of the most widely used metals in various industrial applications. Since they are available for plants’ uptake from the soil, excessive plant exposure to high doses of both metals may be tolerable or not for accumulating species and sensitive species, respectively. Many plants adopt a number of powerful detoxification techniques in their fight for survival. Among them, the antioxidant defence system is a crucial mechanism that helps plants cope with toxic metals, including Li and Ni. Understanding the different approaches that plants use to activate this system can provide insights into how we can improve plant resilience and protect them from environmental stressors. Besides the natural endogenously reacting antioxidant system in the plant’s own body, exogenously applied antioxidants have proven to be effective in mitigating the negative effects of the aforementioned metals. Herein, we review the traditional as well as recent advances used in overcoming the toxicity of Li and Ni to plants.

Water uptake and nutritious mineral utilisation via roots from the soil are the critical requirements for terrestrial plants that have evolved as the major host organisms on the grove of Earth, autotrophically nourishing animals, fungi and many other heterotrophic organisms and continuing to play a crucial role in forming the landscapes of the planet’s biosphere. Minerals taken up from the ground return to the earth via food chains and biome networks through the actions of consumers and decomposers. Through the cyclic usage of inorganic and organic resources, plants and their associates sustain and develop as whole communities. In this chapter, based on such a co-association, or co-evolution, concept, the important interactions between autotrophic plants and the coordinative or competitional fungi and microbes are discussed and emphasised, especially in relation to plant stresses caused by excess levels of Li⁺ and Ni²⁺ ions in land environments.

Li and Ni are gathering more attention, as well as cobalt (Co), because of their importance as very useful elements in industrial activities and sustainable energy for people in the future; however, their use is also accompanied by the incidental threat and concern about their possible increases through release and contamination into land and other environments. Li belongs to the group of relatively abundant alkaline metals (light metals), and Ni is one of the rare and micro-elementary heavy metals. Although their differential and unique impacts on plants and fungi are known, their combinational effects are not well known, so it will be necessary to address the increasing risks in the near future. In this chapter, the existing evidence will be substantiated with details about their bindings and localisations with different bioligands and polymers in the cells of plants or fungi. Taken together, we discuss the importance of complex binding and detoxification systems in plants and the symbiotic associates under combined stresses caused by the two metals as well as others.

Symptoms of plant nickel (Ni) disorders occurring on ultramafic soils resemble those of iron (Fe) deficiency, such as chlorosis. Since plants absorb Ni via root iron transporters, it is expected that Ni would compete with Fe acquisition on the root surface in soils with high nickel concentrations, resulting in Fe deficiency in plants. However, experiments using Arabidopsis thaliana confirmed that the addition of Ni to a hydroponic solution induced an Fe starvation response instead. It has also been observed that Fe content in plant roots increases with Ni content, and in fact, plants from ultramafic soils tend to have higher Fe contents than those from other soil types. This phenomenon, in which Fe deficiency occurs even though Fe is acquired sufficiently, can be attributed to the disruption of the Fe transport system in plants. Nicotianamine (NA) is a biological compound that chelates Fe and is responsible for its transport in plants; however, NA has a higher affinity for Ni than Fe. Because of that, it is predicted that NA, which should be used for Fe transport, is instead bound by Ni, resulting in the inhibition of chlorophyll synthesis in plants under high Ni conditions. Experimentally, plants that overexpress NA genes are more tolerant to high levels of heavy metals, especially Ni.

Soil Ni strongly inhibits plant growth during or immediately after germination. This may be because Ni inhibits the supply of Fe, which is essential for chlorophyll synthesis, and thus prevents the initiation of photosynthesis. An adequate supply of NA may be an essential condition for plants to adapt to ultramafic soils.

The search for environmentally friendly practices and new technologies in order to reduce the ecological impact associated with nickel disposal and pollution remains open. In this sense, phytoremediation stands out as a high-efficiency, eco-friendly green technology for removing pollution from contaminated soil, water and air. It is a form of bioremediation and an economical and sustainable alternative to traditional chemical and physical pollution remediation methods. High metal bioaccumulation efficiency and tolerance are requisites for plants employed in phytoremediation techniques; thus, investigating new aquatic plants with such characteristics is a priority. The antioxidant defence system plays a significant role in providing resistance to plants by protecting labile macromolecules against the attack of free radicals. This ability made possible the use of aquatic plants in technological applications for the restoration of contaminated sediments, solid wastes and organic contaminants. Accordingly, results have demonstrated that Lemna gibba and Ceratophyllum demersum would have the capacity to tolerate and, therefore, resist nickel stress. APX would be a more efficient enzyme in the detoxification of hydrogen peroxide, as its activity was stimulated at higher exposure concentrations. This reinforces the proposal of selecting APX as a good biomarker for the evaluation of the welfare of plants and growth performance. It is important to keep in mind that plant stress tolerance may be improved by the enhancement of the levels of antioxidant enzymes, in particular those related to the application of aquatic plants in the phytoremediation of nickel from wastewaters and industrial effluents.

Human-induced environmental pollution, which has emerged with the increasing population in recent years, has become a global threat. One of the consequences of its rapid and destructive effects is that heavy metals, such as lithium (Li) and nickel (Ni), threaten soil and plant health, and their presence in soil and water poses a risk to both human health and environmental well-being. The purpose of this chapter is to explore the importance of bioremediation in removing Li and Ni from soil and water by investigating various research studies and approaches. Bioremediation is a solution that utilises microorganisms to remove heavy metals by converting them into less toxic forms. Therefore, it is important to carefully select the appropriate microorganisms and optimise the bioremediation conditions to achieve the best results. Moreover, the effectiveness of these techniques depends on various factors, such as the concentration of Li or Ni in the soil, the duration of the remediation process and the environmental conditions.

A detailed knowledge and recent advancements on the sources, speciation, toxicity and chemistry of nickel and its different compounds are discussed in this chapter. Nickel is an essential micronutrient for plant growth, and it is also a component of the enzyme urease, which plays a role in nitrogen metabolism in higher plants. Nickel and nickel compounds are also important for several biological processes in animals and soil/water microbes, and they have many industrial and commercial uses. Nickel is a known heavy transition metal and is found at very low levels in the environment. The vast industrial use of nickel leads to widespread environmental pollution. Higher levels of nickel can affect the photosynthetic function and transpiration of higher plants; it reduces seed germination, root and shoot growth, biomass accumulation and final production. Moreover, nickel toxicity leads to chlorosis and necrosis and may cause oxidative damage in plants. In addition, nickel toxicity degrades soil fertility, which may reduce crop production in the near future. The limited knowledge regarding the mechanisms of nickel tolerance in plants further highlights this fact. Furthermore, it causes many chronic diseases in humans, including allergy, cardiovascular and kidney diseases, lung fibrosis and lung and nasal cancers. The molecular mechanisms of nickel-induced toxicity, which cause the above diseases in humans, are still unknown. Mitochondrial dysfunctions and oxidative stress are mainly considered to play a crucial role in inducing toxicity from this metal. Therefore, we should pay attention in future research to find approachable and prominent ways of minimising the entry of nickel into our environment.

The chapter summarises some essential features and findings related to the toxicities of lithium (Li) and nickel (Ni), which are always present in trace concentrations in food and the environment. These metal elements occur almost everywhere in nature, including in soils, rocks and the atmosphere. Therefore, due attention should be paid to their presence in various substances, including food, water and air. These materials can enter the human body through ingestion of food, drinking water and other routes, such as inhalation and skin penetration. The occurrence of Li/Ni in the environment has increased tremendously recently due to some human activities, especially specific technological processes, which have resulted in an increased presence of these elements in various products and goods. Recently, Li and Ni are gradually being used as main components in Li-ion and NiCd batteries. The first type of battery is mainly used in electric cars, while the less powerful NiCd batteries are primarily used in portable electronic devices and toys.

In addition, the chapter discusses the specific forms of toxicity of these metal elements and their occurrence in some foods. The processes and pathways by which these elements can enter the human organism are also described. They can have severely harmful effects at certain excessive concentrations and amounts. Because of these detrimental impacts, Li and Ni levels should be monitored to enable intervention when their presence exceeds regulatory limits or recommendations. Based on the results of such measurements, effective control mechanisms can then be implemented to minimise their effects on human health, including introducing appropriate measures to protect workers who come into contact with these elements in the workplace. This chapter also describes the actions necessary to regulate these elements’ presence and impose adequate controlling mechanisms and preparations, including those to respond effectively to possible emergencies.

The following section is included:

• Index